1. Field of the Invention
The present invention relates to an analytical method for the determination of the total nitrogen content, principally, in non-aqueous and aqueous liquid samples, and an apparatus suitable for the above analytical method. In view of air pollution caused by nitrogen oxides and nutritional enrichment of water, it has recently become important to determine the nitrogen content of fuel oils, waste water and environmental water.
2. Description of the Prior Art
For analyzing a trace amount of nitrogen in liquid or solid samples, Kjeldahl method, Dumas method and ter Muelen method have hitherto been used. Among these methods, Kjeldahl method has been used with popularity in various fields. This method is superior as a chemical analytical method, but because of its troublesome operations, high grades of technique and skill are required in order for analyzers to obtain accurate analytical values. Moreover, there is too much difficulty in mechanizing this method in order to complete the determination within several minutes, and an apparatus which can be operated simply and rapidly has not yet been developed.
The Dumas method is useful for the determination of nitrogen gas produced by combustion, oxidation and reduction using a mixture of an inert gas and oxygen gas, and it has been simplified by the development of an elementary analyzer for C-H-N. But the analyzer is not suitable for nitrogen microanalysis because its lowest limit of determinable nitrogen content is as high as 0.2% and its sensitivity is insufficient. Besides, apparatuses for nitrogen micro-analysis have been developed by combining the Dumas method and a gas chromatograph with a thermal conductivity detector. However, because oxygen gas is used in these apparatuses, the reducing agents used therein have a shorter life. Furthermore, the apparatuses are complicated in structure and are expensive in cost.
Nitrogen can be determined with a high sensitivity by combining colormetric titration or electro-conductometry with the Muelen method which converts nitrogen compounds to ammonia by hydrogenolysis. Since, however, this combined method uses a large quantity of hydrogen at a high temperature, there is a safety problem in the operation thereof. Moreover, the reduction catalysts lose their activity within a short period of time, and hence, they must frequently be re-activated. Furthermore, this method has a drawback that in case of nitrogen compounds easily decomposable to nitrogen gas such as azo compounds, it shows a slightly smaller value of nitrogen contents than the theoretical value.
There has also been developed an analyzer suitable for the simple and rapid determination of nitrogen. According to this analyzer, an aqueous sample is introduced onto a palladium catalyst heated at a high temperature to bring water molecules into a highly activated state, and the activated water molecules convert nitrogen compounds in the sample to nitrogen gas by their oxidative and reductive actions. But, this analyzer can not be applied to non-aqueous samples.